Social auto-posting (phase 1): daily applicant digest to Telegram/Bale + Instagram caption

Adds a «شبکه‌های اجتماعی» admin section + scheduler that publishes a daily
«کادر آماده‌به‌کار امروز» digest:

- AppSetting: social toggles, posts-per-day, editable header/footer,
  per-channel bot token + chat id (Telegram, Bale), Instagram enable +
  extra hashtags, proxy toggle, last-posted timestamp (+ migration).
- SocialPostService: builds today's talent digest as text, posts to
  Telegram and Bale via their bot sendMessage APIs (proxy-aware), and
  produces an Instagram caption + auto hashtags (role/city based).
- SocialPostWorker: posts N times/day, evenly spaced, self-paced; reads
  settings live so it's togglable without redeploy.
- /Admin/Social: credentials + header/footer + posts/day, live preview of
  today's message, «ارسال اکنون» button, and an Instagram caption pack
  with copy button (semi-automatic — you post the image manually).
- Nav link added.

Telegram/Bale post as TEXT (per request). The Vazirmatn image card for
Instagram is phase 2 (needs SkiaSharp+HarfBuzz + a TTF font).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/JobsMedical.Web/Models/AppSetting.cs

@@ -104,6 +104,32 @@ public class AppSetting
     [MaxLength(200)] public string? VapidPrivateKey { get; set; }
     [MaxLength(120)] public string? VapidSubject { get; set; } = "mailto:admin@hamkadr.ir";
 
+    // --- Social auto-posting: a daily «کادر آماده به کار» digest to Telegram/Bale (text) + an
+    //     Instagram caption/hashtags pack (you post the image manually). ---
+    public bool SocialEnabled { get; set; } = false;
+    /// <summary>How many digests to publish per day (evenly spaced).</summary>
+    public int SocialPostsPerDay { get; set; } = 3;
+    /// <summary>Lines added above/below the auto-generated body (your branding, links, etc.).</summary>
+    [MaxLength(1000)] public string? SocialHeader { get; set; }
+    [MaxLength(1000)] public string? SocialFooter { get; set; }
+    /// <summary>Route the bot calls through the ingestion proxy (Telegram is filtered in Iran).</summary>
+    public bool SocialUseProxy { get; set; } = true;
+
+    public bool SocialTelegramEnabled { get; set; } = false;
+    [MaxLength(200)] public string? SocialTelegramBotToken { get; set; }
+    /// <summary>Channel/chat to post to — «@channelusername» or a numeric chat id.</summary>
+    [MaxLength(120)] public string? SocialTelegramChatId { get; set; }
+
+    public bool SocialBaleEnabled { get; set; } = false;
+    [MaxLength(200)] public string? SocialBaleBotToken { get; set; }
+    [MaxLength(120)] public string? SocialBaleChatId { get; set; }
+
+    public bool SocialInstagramEnabled { get; set; } = false;
+    /// <summary>Extra hashtags appended to the generated Instagram caption (space/line separated).</summary>
+    [MaxLength(1000)] public string? InstagramHashtags { get; set; }
+
+    public DateTime? SocialLastPostedAt { get; set; }
+
     public DateTime UpdatedAt { get; set; } = DateTime.UtcNow;
 
     /// <summary>Split a textarea (newline/comma separated) into trimmed non-empty items.</summary>